Office 98 and 2001 run on OS 9.
Office X and Office 2004 run on OS X.
Upgrading to OS X (aka Jaguar, Panther) is a serious undertaking that would
require a lot of new software and probably extra memory for your computer,
if it is even OS X compatible. You may want to wait to upgrade OSes until
you buy a new computer, although OS 9 is now obsolete and no new software
will be developed for it. [does anyone have a link to a nice short overview
of the whole OS 9 and OS X situation and what it means, for the
un-computer-savvy, by the way?]
It will be quicker and less expensive to return Office 2004 and look for a
copy of 2001 or 98, I believe both are still being sold new at some Mac
resellers and you may be able to get a cheap used copy since they are also
obsolete. Even if you find you can't return Office 2004, it will probably
still be less expensive.
You would find the system requirements for Office 2004 at mactopia.com, the
website for the Mac division of Microsoft.
